Innovative Methodology Arteriolar smooth muscle Ca dynamics during blood flow control in hamster cheek pouch

Brekke, Johan Fredrik, William F. Jackson, and Steven S. Segal. Arteriolar smooth muscle Ca dynamics during blood flow control in hamster cheek pouch. J Appl Physiol 101: 307–315, 2006. First published February 2, 2006; doi:10.1152/japplphysiol.01634.2005.—Intracellular calcium concentration ([Ca ]i) governs the contractile status of arteriolar smooth muscle cells (SMC). Although studied in vitro, little is known of SMC [Ca ]i dynamics during the local control of blood flow. We tested the hypothesis that the rise and fall of SMC [Ca ]i underlies arteriolar constriction and dilation in vivo. Aparenchymal segments of second-order arterioles (diameter 35 2 m) were prepared in the superfused cheek pouch of anesthetized hamsters (n 18) and perifused with the ratiometric dye fura PE-3 (AM) to load SMC (1 M, 20 min). Resting SMC [Ca ]i was 406 37 nM. Elevating superfusate O2 from 0 to 21% produced constriction (11 2 m) that was unaffected by dye loading; [Ca ]i increased by 108 53 nM (n 6, P 0.05). Cycling of [Ca ]i during vasomotion (amplitude, 150 53 nM; n 4) preceded corresponding diameter changes (7 1 m) by 2 s. Microiontophoresis (1 m pipette tip; 1 A, 1 s) of phenylephrine (PE) transiently increased [Ca ]i by 479 64 nM (n 8, P 0.05) with constriction (26 3 m). Flushing blood from the lumen with saline increased fluorescence at 510 nm by 45% during excitation at both 340 and 380 nm with no difference in resting [Ca ]i, diameter or respective responses to PE (n 7). Acetylcholine microiontophoresis (1 A, 1 s) transiently reduced resting SMC [Ca ]i by 131 21 nM (n 6, P 0.05) with vasodilation (17 1 m). Superfusion of sodium nitroprusside (10 M) transiently reduced SMC [Ca ]i by 124 18 nM (n 6, P 0.05), whereas dilation (23 5 m) was sustained. Resolution of arteriolar SMC [Ca ]i in vivo discriminates key signaling events that govern the local control of tissue blood flow.